1. Field of the Invention
The invention relates to storage of hydrogen and somewhat more particularly to a material comprised of a amorphous silicon for storage of hydrogen and a method of producing such material.
2. Prior Art
With an increasing scarcity of fossil fuel, the development of new energy sources are gaining importance, among them, inter-alia, the regenerative energy sources. Hydrogen, as an energy source, has an advantage in that it is available in virtually unlimited quantities from water. With suitable handling, hydrogen is also a reliable and pollution-free fuel, which can readily release its energy through oxidation. A volume of 22.4 standard liters of hydrogen gas contains, in accordance with the reaction: EQU H.sub.2 +1/20.sub.2 .fwdarw.H.sub.2 O+68.3 kcal
an energy quantity of 0.08 kWh.
For economical storage of large energy quantities, it is necessary to store hydrogen in a highly concentrated form so as to keep the storage volume as small as possible. It is also fundamentally important that the stored hydrogen be readily and reliably transportable. Because of the considerable proportion which non-rail traffic has of present fossil fuel consumption, there will also be a considerable significance attributed to hydrogen technology in future conveyance means (for example hydrogen tanks for motor vehicles equipped with a gas motor).
Storage of hydrogen under normal pressure, with the projected energy requirements, would require extremely large volumes, whereas present storage of hydrogen under high pressure (250 bar) in the form of large pressure bottles or tanks is impractical, expensive and dangerous. However, metal alloys are known which releasably absorb large quantities of hydrogen and thus can be utilized to store hydrogen. Best known examples of such alloys include ferro-titanium-hydride, FeTiH.sub.1.7, magnesium-nickel-hydride, Mg.sub.2 NiH.sub.2 and magnesium-hydride, MgH.sub.2. The very heavy ferro-titanium-hydride releases hydrogen at 20.degree. C. at a pressure of 1 bar, the lighter magnesium-hydride must be heated to 300.degree. C. before it will release hydrogen. An ideal hydrogen storage material, which is lightweight and economical and which also releases absorbed hydrogen at relatively low temperature has not yet been discovered.
In solar cell technology, D. E. Carlson et al. in an article appearing in J. Electrochem. Soc., Solid-State Science and Technology, Vol. 126, (1979) pgs 689-691, suggests that thin layers of amorphous silicon can absorb up to 50 atomic percent hydrogen. The maximum absorption capacity of amorphous silicon (generally referred to as a-Si) for hydrogen will be above these values. However, the maximum hydrogen absorption capacity of a-Si has not yet been investigated in solar cell technology because relatively low concentrations of hydrogen are adequate for a-Si.
A safe and reversible storage and transportion of concentrated hydrogen with a storage medium comprised of amorphous silicon (a-Si) is described and claimed in commonly assigned German Offenlegungsschrift 28 55 413, which generally corresponds to U.S. Pat. No. 4,265,720. In accordance with these teachings, generally, hydrogen is stored in amorphous silicon which has been deposited in thin layers on a substrate material, such as quartz or steel.